The present invention relates to a method of inspecting defects which exist in the surface of an object to be inspected, including steps of discriminating microscopic defects from foreign substances and classifying the defects which are located in the surface of the object.
Inspection of semiconductors, which has been conventionally carried out to find defects in the surface of the semiconductor, such as for example a silicon wafer, is typically accomplished by performing an exterior inspection for visually locating flaws. However, in contrast with this type of visual inspection, the inspection of GGG wafers has conventionally been done by skilled workers using microscopes. The reason for this is that a GGG wafer requires faultlessness and high purity in the degree of less than one defect in one single crystal in order to prevent an undesirable influence on subsequent steps for the formation of magnetic film bubbles. That is, in the conventional inspection of a GGG wafer, visual inspection using a microscope with a 50X magnification has been carried out to perform discrimination between defects as well as foreign substances, and classification of defects in order to distinguish processing-induced defects from crystal defects.
Some defects which are low in contrast, are 2 to 10 .mu.m in depth so that the visual inspection should be made using a microscope of as large a magnification as 100X to 400X as necessary. Therefore, the above-mentioned inspection of GGG wafer is a time-consuming procedure which causes fatigue of the worker's eyes so that they are apt to overlook the defects.